Human coronaviruses (HCoV) were initially identified as major causes of acute respiratory tract disease in the 1960's. The epidemiology of two HCoV, OC43 and 229E, was established using only serological methods, due to difficulty culturing the viruses. Three new HCoV have been described in the last three years [1-4]: severe acute respiratory syndrome coronavirus (SARS-CoV) [4], human coronavirus Netherlands (HCoV-NL) [1, 2], and human coronavirus Hong Kong (CoV-HKU1) [3]. Each of these new viruses has been described in association with lower respiratory tract illness (LRI). The discovery of these viruses has renewed interest into the previously known HCoV OC43 and 229E which were known to cause upper respiratory tract illness (URI). HCoV OC43 and 229E have also been associated with LRI like the newly discovered coronaviruses. However, there are no published large-scale epidemiologic studies of OC43 and 229E using highly sensitive molecular diagnostic methods. The objectives of this study are to define the prevalence and clinical illnesses associated with the new human coronavirus HCoV-NL and the prototypic HCoV, OC43 and 229E, over a 20-year period in a cohort of over 2,000 previously healthy outpatient children. We also will determine the genetic variability of these viruses by amplifying and sequencing the HCoV spike protein gene. The Vanderbilt Vaccine Clinic (WC) clinical database and sample archive provide us with the tools to accomplish these goals. The WC provided comprehensive medical care to a large cohort of outpatient children who routinely had surveillance cultures of respiratory secretions and serum samples obtained, thus thousands of nasal wash and serum specimens are available for study, along with robust, prospectively collected clinical data. This provides a unique opportunity to investigate the importance of emerging human pathogens. Our preliminary data using samples from the WC indicate that coronaviruses are a significant cause of respiratory tract infection in children with a spectrum of illness and morbidity. [unreadable] [unreadable] [unreadable] [unreadable]